This invention relates generally to gas turbine engines and more particularly to exhaust duct liner attachment systems and methods. In gas turbine engines, it is necessary to protect exhaust ducts with an insulating shield in order to prevent heated core gases from damaging the exhaust ducts. Typically, exhaust ducts are made from titanium or titanium alloys and have temperature limits in the vicinity of 400° F. (204.4° C.). Exhausted core gases can reach temperatures upwards of 3500° F. (1648.89° C.). It is, therefore, necessary to line exhaust ducts with a material capable of withstanding the peak temperatures of the core gases and that prevents the exhaust duct from reaching its temperature limitations.
For particular operations, particularly in military operations, it is desirable to have aircraft with conventional take-off and landing (CTOL) capabilities, and short take-off, vertical landing (STOVL) capabilities. CTOL requires conventional thrusting of the aircraft in the horizontal direction, while STOVL requires thrusting of the aircraft in vertical and intermediate directions. Some dual capability aircraft designs thus employ variable direction exhaust ducts, such as three bearing swivel ducts (3BSDs), for directing thrust produced by the exhaust nozzle in both the horizontal and vertical directions. Variable direction exhaust ducts typically comprise multiple co-axial exhaust duct segments having angled junctions, whereby the segments can be rotated with respect to each other to redirect the direction of thrust. The exhaust duct segments interface through swivel bearing joints, which extends partially into the assembled exhaust duct. This has the effect of restricting the diameter of the exhaust duct near the swivel bearing joints. In order to properly pre-load the swivel bearings, it is typically necessary to assemble the exhaust duct segments before attaching exhaust duct liners to the exhaust duct segments. It is, therefore, necessary to have an exhaust duct liner suspension system that can be inserted past the swivel bearing joint in, and secured to, an already assembled exhaust duct. This typically requires insertion of fasteners into the interior of the duct from the exterior, which can lead to difficulties in aligning fasteners with the suspension system, and dropping of fasteners into the exhaust duct, from which they are not easily recovered. It would be desirable to simplify the installation process of such suspension systems to, for example, reduce installation time and insure proper installation alignment.